joshuaho96

No, but I'd rather not spend 5000 USD on a stroker kit only to discover that the engine peaks in power undesirably early. -5s are too small for 2.6L, but the GT3-SS is so small that it has trouble holding boost out to 7000 RPM even with 2.6L. I have a feeling that if you stroke it out to 2.8L it's going to be even worse in that regard.

Gran Turismo Sport seems to do a pretty good job of simulating the R32/R33/R34 GT-Rs.

I was under the impression that if a turbo is already choking the engine above a certain RPM, additional displacement would just shift the power curve down some amount of RPM. Is this not the case?

Yes, if you're going to go past a 2.8L stroker on an RB26 block it definitely makes sense to go to an RB30 bottom end instead, which has a much longer 152.7mm conrod. Even with a 3.4L, 94mm stroker kit on an RB30 you're still at 1.62 rod ratio which is roughly what the RB26 is at stock. More cubes is better for performance no doubt, my concern is that going to a 2.8L stroker on the RB26 means you might increase piston side pressure to unfavorable levels, and that going to a 121.5mm rod means you compromise the piston design. Shorter compression height means there's less room for the piston rings, either the top ring gets closer to the crown, the oil control rings get closer to the piston pin bore, or the rings have less spacing. Personally, I'm really hoping the turbo I selected is small enough to not require agonizing over this issue any further.

Stroker kits are either 119.5mm or 121.5mm, but the stroke in both cases increase to 77.7mm. So you're picking between a 1.56 rod ratio or 1.54 rod ratio. Either way it's on par with the B18 used in the Integra Type R, which seems to be pretty close to the edge of what is considered safe. The longer conrod length kits use a different piston design to get everything to work. Anyways, my plan has always been to target low power and focus on balance. I expect with the HKS GT3-SS turbos I selected it will already nose over well before 7000 RPM even with 2.6L displacement.

Is 2.8L stroker on the RB26 really a wise move to go for in a rebuild? I get the impression that the RB26 was already a stroker motor from the factory and was originally intended to be a 2.4L. 2.8L would cause the conrod/stroke ratio to get even more unfavorable. I'm currently planning out an RB26 build and this issue has made me go back and forth on whether a stroker kit is really wise.

doublepost

Base timing on an RB26 is 20 degrees BTDC. If you actually have your base timing at 10 deg BTDC then commanding 26-28 degrees means you're actually commanding 16-18 degrees of timing. As others have said, it's also possible that you're knocking and not hearing it. Is the OEM knock sensor particularly insensitive or something? I was under the impression that a properly set up knock sensing setup (bandpass set up with correct bandwidth + peak, crank window appropriately set) is on par with what human ears can do.

What kinds of compromises are involved in fitting an RB30 into the R32?

45M yen price tag. Well outside the budget of anyone that would be posting here I presume.

Are they ever getting around to the double VCAM setup they claimed to be working on?

The question is really more why do you want a billet block? They're designed for 1200+ hp builds. The liners are extremely thick and the water jacket doesn't do as much as it does in the stock block which is a closed deck that reduces coolant flow. You should really consider what this car is going to be used for. If it's going to be idling in traffic all day that means keep the power relatively low to reduce cooling load on the engine, keep the OEM water pump, big radiator, stock clutch fan with fan shroud, proper radiator ducting. All of those requirements point towards either OEM or N1 block. It would be cool to have some billet aluminum block tailored for say 600 whp max as a "street oriented" block but the people willing to put down 10-13k USD on a billet block usually want big power, not just removing ~30 kg from the front of the car.

Now that we've derailed this thread about billet blocks, does anyone know if the PPG or stock ratios are better for the stock 5 speed in the R32/R33 GTRs? I'm looking for a synchro transmission and I don't think I can afford the expense of doing a V160 swap properly.

If the car starts just with a normal key and no transponder/remote required there's no real security system.

I'm planning on putting in a step 1 VCAM, does it make sense to change the exhaust cam as well or just leave it?

Yeah, the first step is fine. I would just install a Nismo oil separator or comparable while you're in there. Low boost, tune, take it easy for a while and make sure the engine is healthy. Dipstick vent and oil cap vent are really last resorts, don't bother unless you're really having issues with blowby, which you shouldn't at low boost and an internally stock engine. If you're going to run a high flow oil pump you should go with an extended sump. The two go together, generally speaking.

More boost creates more blowby, which stresses the PCV system more. More blowby means more oil spitting out the breathers. The crankcase vent mods are really to solve that issue, track use just means spending more time at high boost. Street use just implies you're not spending very long at high boost. If you're going down the road of a built engine think carefully about the trade-offs there. 2618 forged pistons are very tough and make big power but they do not live long lives. For something that is street-first you probably don't want to have an engine that has quite a lot of piston slap and needs to be carefully and lovingly warmed up, it's better to have a piston that calls for a tight piston to wall clearance for street use. Don't wildly overbuild an engine for way more power than you want. Tight piston clearance also helps with reducing blowby, so for track use if you aren't too wedded to huge power it'll make oiling less of a headache. Really, every time I think about these issues with the RB26 the real solution is to sell the car and get a 996 Turbo but I have some kind of brain damage that keeps me from doing the obvious, cost effective solution. Does anyone know if the Tarmac Solutions sump is going to be enough with just 1.5L extra? I'd like to only bump up to ~6L of oil capacity instead of 8-9L but I'm not sure if it's a good idea.

Modifying engines is hard, if anything it's harder if you intend for this to be a street build that can survive track punishment. Deleting power steering/AC/etc is a much harder pill to swallow to go dry sump, ripping out your trunk liner to fit an Accusump is a lot less palatable for a street-first kind of build, etc. You have to decide what this car is going to be. If you want it to survive on the track with wet sump you want to turn down the boost, run less aggressive tires, etc. If you want to have 500+ whp for hard drag launches with slicks and hard track use but also street usability something has to give for practicality. The RB26 is really not a great engine in that regard, modern engines are amazingly better at doing what you want to do. Don't forget that to survive races with 600 hp the RB26 had swinging pickups and all kinds of other craziness for the oiling system, the stock RB26 has basically none of that.

Biggest thing to worry about with these engines is crankcase ventilation. You can have a huge pump pushing tons of oil on the oil feed but you'll ventilate the block if excessive crankcase pressure keeps oil from returning to sump fast enough. That's really what causes the "oil stuck in head" issue. Nissan figured this out with the R35 GTR, which is why the oil pump has both a scavenge pump and a pressure pump as well as significantly improved crankcase ventilation. The pressure pump is your usual oil pump, the scavenge side is on the oil return ports trying to forcibly suck air/oil down the return ports and force the returned oil into the pickup, so it's a "hybrid wet sump" in that regard: https://conceptzperformance.com/aam-competition-oil-pump-isr-treatment-nissan-gt-r-09-r35-aam-isr_p_7433.php In the context of a wet sump RB26, you can either try and improve the crankcase ventilation system as-is with more breathers. I haven't been able to examine the breather fittings/hoses yet but one "easy" mod may be to put in a checkvalve on the crossover tube and then drill out any restriction that may be present in the stock breather fittings. That would keep fresh air from bypassing the crankcase when on vacuum but allow for maximum flow when on boost. I suspect that you would ultimately need to add another crankcase breather directly off the crankcase though.

If you're concerned about imminent catastrophic failure, monitor your engine by doing oil analysis and/or cut open your oil filters to look for metal filings. Leakdown/compression is also good to know, if either are poor you want to rebuild before turning up the power. Rebuilding an engine is simpler and less likely to go wrong when it hasn't spun a bearing/bent rods/valves/etc so if you see metal shavings in the oil filter or high bearing content in the oil stop driving the car and get the engine pulled. Once you've built up a baseline over a few oil changes you can crank up the boost and see if the engine is surviving the same way. Also check coolant and oil levels regularly to make sure you aren't leaking/burning anything. It's a huge waste of time to pull and tear down an engine just to inspect the bearings. Cylinder bore condition + piston condition can be inspected by pulling spark plugs and borescoping it. Oil analysis is relatively cheap, so is cutting open an oil filter.

The point is the transient response. There is a transition period between idle air + timing and the new mass flow rate + timing. Lower airflow at idle makes the engine tend to respond more in both directions. Additional loads like AC compressors can cause the engine to stall, adding more air will tend to make the engine want to race up. More air means transients are smoothed out more. I'm not saying that we should all go out and change base timing to 30+ degrees on our engines, base timing for idle is often set where it is to ensure that the engine won't stall. What's important is understanding the trade-offs between setting advanced/retarded base timing and whether the assumptions the OEM uses to set base timing are still true for your setup.

It's a matter of proportion. "vacuum is higher" as an explanation suggests that the tail wags the dog. If you need less air to idle, then when you crack open the throttle the air provided by the throttle has a larger proportion compared to the AAC bypass air. Suppose you need 1.5g/s to idle with 30 degrees of timing at idle, but 6g/s to idle with 10 degrees. If you crack open the throttle to get 20g/s of airflow then the engine will suddenly receive 13.3x more air in the first case, but only 3.3x more air in the second case. The difference in engine response to 3.3x more air is quite sluggish compared to 13.3x more air. Important thing to remember is that you need, need to have enough reserve torque to control idle speed. Adaptronic has published a video talking about this issue, which maps with what I've experienced with my tuning experiments:

The R34 GT-R valuations, especially for the rare variants, have never been tethered to what the car actually is. Every time I look at the frame of an R34 Skyline it's very clear that it is basically the exact same thing as an R33 Skyline. What is actually remarkable is that you can see the progression of cost-cutting on the undercoating from R32 -> R33 -> R34 Skyline. The R34 has the least and has the same rust issues as the R33 but also the extra brackets on stuff like the carbon fiber diffuser is even worse for rustproofing and tend to be swiss cheese after 20 years. Effectively the main differences between the R33 and R34 are some bolt-on suspension arms/bushings, some chassis reinforcement pieces in places like the trunk floor, the divider between the rear seat and trunk, the base of the B pillar, etc. There's also the 6 speed Getrag, the slightly revised RB26 (different CAS, ball bearing ceramic turbos, smart coils, etc), and slightly improved HICAS logic. I doubt most people are really interested in keeping HICAS but if it matters enough it's probably possible to adapt the R34 HICAS controller over to an R33. I'm sure this sounds like sour grapes but it's more like bewilderment because there seems to be an obvious backdoor to have a car that drives like the R34 GT-R but for much less money.

You should try it for yourself, the difference in linearity and throttle response is noticeable. If you need 5 g/sec AAC bypass air to idle and you crack open the throttle, the difference is very noticeable compared to if you were to get it down to 1.5 g/sec. I've had subtle vacuum leaks happen before and the engine won't respond nearly as much to the throttle until it's fixed even though timing/fueling was all in a good state and the tune was speed density.

MBT is maximum brake torque timing. It's the value that maximizes engine efficiency for that operating point, assuming you don't get limited by knock first. A stock RB26 should idle warm around base timing with no accessories and nothing else going on. It will jump to more or less timing to control the idle. The more timing you can dial in at idle the less air you need, the less air you need the more control authority the throttle has. The AAC valve is basically a controlled vacuum leak. You want to reduce it as much as possible so that the engine responds more to your pedal. There are limits to this though because idle requires the ECU to constantly adjust timing/airflow/fuel to keep it stabilized. If you add too much base timing and pull out too much air the ECU won't be able to compensate for sudden drops in engine RPM and the likelihood of a stall rises.